India
Its steaming streets crammed with vendors, pedestrians, and iconic Ambassador taxis, Kolkata throbs with some 16 million people—and more pour in every day from small towns. In 1975 only three cities worldwide topped ten million. Today 21 such mega cities exist, most in developing countries, where urban areas absorb much of the globe's rising population.]]>

England
Glowing furnace bright at night, London became the world's largest city during the coal-powered industrial revolution, a tipping point for the steep rise of Earth's population. Wealthy countries use many times more resources per capita than poorer nations, but as global incomes rise, increased consumption may stress the planet more than population growth.]]>

Spain
Immigrants like these Indians at a Sikh festival in Barcelona are bolstering Europe's stagnant population growth rate. Around the world, the childbearing decisions of young women will determine whether global population stabilizes or not. Research shows that the more education a woman receives, the fewer children she is likely to have.]]>

Russia
A nurse at the Centre for Family Planning and Reproduction in Moscow holds up a newborn for excited family members waiting outside. The government is thrilled by births as well. Russia's population keeps falling and is now 142 million, down from its peak of 148 million in the 1990s.]]>

http://pictopia.com/perl/ptp/natgeo?photo_name=1361062/2011/01/7-billion/img/05-america-bundled-newborns-714.jpg/2011/01/7-billion/img/billion-60-05.jpgPhotograph by John Stanmeyer

United States
Bundled newborns on September 1, 2010, are arranged for a portrait at Orlando's Winnie Palmer Hospital, the second busiest birth facility in the U.S. Unusual among industrial nations, the U.S. has a comparatively high fertility rate, due in part to the significant rate of teenage pregnancies and a steady influx of immigrants. By 2050 America's population is expected to top 400 million.]]>

Kenya
In a Nairobi slum Mary Wanza, a single mother earning three dollars a day, makes porridge for ten children, some hers, others grandkids and orphans. Wanza, 41, gave birth to the first of seven at age 15. Fertility rates remain high in sub-Saharan Africa; Kenya's rate fell from eight to five births per woman between 1960 and 2000 but has since declined only to 4.6. The global average is 2.5.]]>

Turkey
Not bothering to unpack, an Iraqi family displaced by war awaits orders to move from temporary housing in Istanbul to a "satellite city" designated for refugees and asylum seekers while authorities consider their resettlement applications. Many of the world's 11 million refugees and asylum seekers—persons uprooted by conflict or persecution—live in a similar limbo, often unable to gain legal status in a new home country.]]>

Russia
Traffic is light—a horse cart with grain, a puppy in pursuit—on a road passing an abandoned granary and church in Novotishevoye, one of thousands of Russian villages depopulating as people move to cities and have fewer kids. To combat a low birthrate, the government has promised to pay $11,500 to women who have a second child.]]>

Japan
A talking robot helps 69-year-old Nabeshima Akiko shop in a test conducted by researchers from Keihanna Science City near Kyoto. Making up 23 percent of the population, the 29 million elderly in Japan far outnumber the young, an unprecedented situation that raises concerns about who—or what—will support the old in the years ahead.]]>

Italy
An elderly woman has a front-window view of a Good Friday procession passing by her home in Orosei, on the island of Sardinia. In an aging nation, Sardinia's population is especially old, with one of the world's highest ratios of people over a hundred years old. Centenarians on the island have recently numbered as many as 187.]]>

Venezuela
Sharing a hillside with high-rise apartment dwellers, children dance at a shop in one of the squatter communities that ring Caracas, a city of three million. One in seven people on Earth lives in slums today. Providing them with better housing and education will be one of the great challenges facing a world of seven billion people and counting.]]>

United States
A new house went up every 20 minutes during the 2004 building boom that seized Las Vegas and its sprawling suburbs, like Henderson. The American lifestyle—characterized by gas-thirsty cars and big houses using lots of electricity—contributes to the country's energy appetite; its carbon emissions are four times higher than the global average.]]>

China
Using every fertile inch, farmers harvest rice in the hills of Yunnan Province. High-yield seeds and ample fertilizer allow China to feed its billion-plus people on less than 10 percent of the Earth's arable land. Producing enough food as global population grows is possible, but doing so without exhausting finite resources, especially water, will be a challenge.]]>